Process for the nitration of halobenzenes



3,7d,3? Patented Jan, 29, 1%53 3,ti7d,ti37 PRGtIEdS FER THE NXTRA'HUN FHALSBENZENES Robert I. Leib, Kir'irwood, Md, assignor to MonsantoChemical Company, dt. Louis, Mo., a corporation of Delaware No Drawing.Filed Feb. 5, 1969, Ser. No. 6,359 19 Claims. (Cl. 26%-646) Thisinvention relates to an improved process for the preparation ofnitrohalobenzenes by the nitration of the corresponding halobenzene,whereby a more favorable isomer distribution is obtained.

The present methods used in the preparation of nitrochlorobenzene, forexample yield a mixture of the para and ortho isomers, in which thepara/ortho ratio is generally around 1.7, i.e. it contains 63% paraisomer and 37% ortho isomer. Because of the current and projected demandfor the para isomer, a great oversupply of the ortho isomer will resultif this need for the para isomer is fulfilled by using the currentmethods of making nitrochlorobenzene.

It has been found that the isomer distribution in the nitrohalobenzeneproduct is favorably influenced when the nitration of a halobenzenecompound is carried out in the presence of an amine salt. The presenceof even small amounts of an amine salt markedly influences the isomerdistribution in a nitrohalobenzene product and this effect is stillobtained when a high concentration of amine salt is employed, i.e. Where3 moles of amine salt per mole of halobenzene are used. Moreover, theamount of the desired isomer obtained when the nitration is carried outin the presence of an amine salt is greater than the amount obtained inthe absence of an amine salt regardless of the nitrating agent ornit-rating temperature employed.

The nitrating agents which can be employed in the process of thisinvention include, for example, the conventional mixed acids, i.e.mixtures of nitric acid and a dehydrating acid such as oleum or sulfuricacid, which contain from about 20% to about 60% by Weight of nitric acidand from about 75% to about 35% by weight of sulfuric acid, the balancebeing made up by Water; a mixture of ethyl nitrate and sulfuric acid,nitrogen pentoxide and other strong nitrating agents which areconventionally employed in the nitration of a halobenzene. Mixed acidscontaining from about 30% to about 40% by Weight of nitric acid and fromabout 65% to about 55% by weight of sulfuric acid are preferred for theprocess of this invention.

The amine salts which are useful in the process of this invention arethe amine salts of nitric acid or sulfuric acid or mixtures thereof. Anyamine salt can be employed, however the amine salts in which the organicresidue is not subject to nitration or oxidation under the nitratingconditions employed are preferred for the purposes of this invention.

Illustrative examples of amines which can be employed in the process ofthis invention in their nitrate or sulfate form are the primaryaliphatic amines such as methylamine, ethylamine, propylamine,isopropylamine, n-hexylamine, dodecylamine, tetradecylamine,hexadecylamine, etc.; secondary aliphatic amines such as dimethylamine,diethylamine, diisopropylamine, di-Z-ethylhexylamine,N-methyl-dodecylamine, N-ethyl-pentadecylamine, etc.; tertiary aliphaticamines such as trimethylamine, triethylamine, tripropylamine,tributylamine, trioctylamine, N-methyldiethylamine,N-ethyldipropylamine, N-pentyldidodecylamine, N-N-diisobutylhexylamine,etc.; the aliphatic polyamines such as 1,4-propylenediamine,1,3-ethylenediarnine, 1,2-butylenediamine, etc.; the cycloaliphaticamines such as cyclopentylamine, cyclohexylamine,2,4-dimethylcyclohexylamine, Z-methylcyclohexylamine,4-ethylcyclohexylamine, cycloheptylamine, 4-methylcycloheptylamine,dicyclohexylamine, cyclohexane 1,3-diamine etc.; mixedaliphatic-cycloaliphatic amines such as N-ethylcyclohexylamine,N-butylcyclohexylamine, N-propylcycloheptylamine,N,N-diethylcyclohexylamine, etc.; the heterocyclic amines such aspyrrolidine, 2-methylpyrrolidine, Z-ethylpyrrolidine,2,4-dimethyl-3-ethylpyrrolidine, 1,2,2- trimethylpyrrolidine,3,4-dimethylpyrrolidine, pyrazole, Z-methylpyrazole, Z-ethylpyrazole,2,5-dimethylpyrazole, 2,3,5-trimethylpyrazole, 3,5-dimethylpyrazole,imidazole, l-ethylirnidazole, 4-methylimidazole, 1,2,3-triazole,4,5-dimethyl-1,2,3-triazole, 1,2,4-triazole, pyridine, 2-picoline,3-picoline, 2-lutidine, parvoline, rubidine, 3-picoline, 2-pipecoline,3-pipecoline, 4-pipecoline, 1,2-dimethylpiperidine,1,4-dimethyipiperidine, 2,6-trimethylpiperidine,Z-methyl-S-ethylpiperidine, morpholine, Z-methylmorpholine,triamorpholine, 2-ethylmorpholine, pyrazine, quinoline, isoquinoline,2,4-dimethylquinoline, 4-ethylquinoline, 2,5-pyridoquinoline,1,3-oxazole, 1,2,4-0xadizine, 1,4,2-oxadiazine, indoloindole,1-indeno-1,2b-pyridine, acridine, l-methylacridine, Z-methylacridine,1,3-dimethylacridine, 2,5-dimethylacridine, phenanthridine,Z-methylphenanthridine, Z-ethylphenanthridine,1,3-dimethylphenanthridine, 5,6-benzoquinoline, 6,7-benzoquinoline, 7,8-benzoquinoline, 6,7-benzoisoquinoline, naphtho-2,3h-quinoline, etc.

While the amines containing an aromatic residue are generally subject tonitration, they may be used in the process of this invention if anexcess of the nitrating agent is employed. Illustrative examples ofamines containing an aromatic residue are, for example, aniline,naphthylaniline, phenylenediamine, 3,5-dimethylaniline,2,3,6-triethylaniline, phenanthrylamines, mixed coal tar bases,N-methylaniline, diphenylamine, N-octylphenylamine,N-butyl-p-methoxyaniline, N-cyclohexylaniline, N-Z-ethylhexylaniline,N-octylbiphenylamine, diuaphthylamine, N-rnethyldiphenylamine,N-butyldiphenylamine, benzylaniine, phenylethylamine,2,4-dimethylbenzylamine, 3-butylbenzylamine, 4-t-butylphenylethylamine,N,N-dimethylbenzylamine, N,N-diethylbenzylamine,N,N-dipropylbenzylamine, N-ethylbenzylamine, N-hexylbenzylamine, andtheir homologues and analogues.

The aforementioned amines may be further substituted by one or moresubstituents. Typical but not limitative of such substituents are nitro,carboxy, the halogens, such as chlorine, bromine, iodine and fluorine,and other nonreactive substituents.

The lower aliphatic amines which have a tertiary allryl group attachedto the nitrogen atom constitute a preferred class of aliphatic amines tobe employed as their acid salts in the process of this invention. Theseamines have the following structure:

wherein R is an alkyl radical containing from 1 to 18 carbon atoms, e.g.methyl, ethyl, propyl and butyl.

The acid salts of heterocyclic amines containing a tertiary nitrogenatom also constitute a preferred class of acid salts to be employed inthe process of this invention.

The acid salt can be prepared separately or it can be prepared in situ.For example, the free amine can be added to the nitration reactionmedium and the amine converted to the acid salt form by the addition ofa suificient excess of nitric or sulfuric acid to tie up the free amine.Moreover, a preferred method of carrying out the process of thisinvention involves adding concentrated sulfuric acid to a mixture of thehalobenzene and the free amine. After all of the amine has beencon- 3verted to the acid sulfate form, the mixed acid nitration is thenstarted.

Effective concentrations of the amine salt in the process of thisinvention vary in Wide ranges depending upon the tains the amine saltand the spent acid may be dehydrated and then recycled.

The manner of carrying out the process of this invention and theexcellent results achieved therefrom will be result desired, in thatextremely low amounts, e.g. 0.05 5 further apparent from the followingspecific examples in mole of amine salt per mole of halobenzene to benitrated which all parts and percentages are by weight unless otherwillproduce the para directive effect. Moreover, as the wise specified.

number of amine salt groups per molecule is increased, EXAMPLE 1 theamount required to produce a given result is reduced proportionately. Ahigher para isomer concentration in T 5 Well surfed mlxture of Parts(140 mole) of the nitrohalobenzene product is achieved when the con- P Pf of Chlorobenzene there centration of amine salt is within the range offrom about 15 added dYOPWISe While eeol'lngi Parts mole 0.5 to about 2moles per mole of halobenzene to be H2$ U of 953%? u f nc acld. A whiteflocculant prenitrated. It is even more preferred to employ about 1.0elpltate of pg fulfate results- Thls Slurry 18 then mole of amine saltper mole of halobenzene to be nitrated. l5 heatefl to I end 190 P e molea) More than 3 moles of amine salt per mole of halobenzene of mlhedfield, I I g 33% by weight HNO 55% to be nitrated can be employed,however no significant inby Welght a 4 and 12% Water, l f Slowly ecrease in para isomer content or yield results over that e 110111: P PAfter the field the l'eae'llen m is obtained with 1 to 2 1 mixture ismaintained at a temperature of 50 to 55 C.

A preferred embodiment of this invention is the process about two e Theresulting mlxtul'e 15 then P for the preparation ofparanitrochlorobenzene which commiffed to Separate Into 1W0 P e and hbottom pe prises nitrating chlorobenzene with a mixed acid comprisaeld e15 -(R The 011 layer 15 Washeq Wlth ing 30% to 35% by weight of nitricacid, 55% to 60% by two a gl contamms P of Water; two ahquots weight ofsulfuric acid and 15% to 5% by Weight of containing 200 parts by weightof a 5% sodium carbonate water, in the presence of a sulfate salt of alower aliphatic Sohlhon and he y Wlth two addlhehal ahquots amine havinga tertiary alkyl group attached t th it The washed oil is then heated atreduced pressure to regen ato thereof. A furth preferred b di i move anyunreacted chlorobenzene and the resldual water. volves the use of asulfate salt of a heterocyclic amine hav- There is obtelhed 494138118 0fnitroehlorobehlehe- The ing a tertiary nitrogen atom. product contains ps Those skilled in the art will recognize that this inven- The followingtable represents additional examples of tion is not limited to specificreaction temperatures since the presentmvention, Wherem the pp Procedurethis process can be carried out at a tempearture of from ingredients ofExample 1 utilized eXleePt es 3 (3 to 100 C or more, A reactiontemperature specified in the table. Generally, the temperature of the of30 C. can be maintained, for example, b 1 reaction, the reaction timeand the molar ratio of nitric ing a cooling bath comprising a slurry ofsolid carbon acid to chlorobenzene are the same as in Exampl dioxide inacetone and using chloroform as a reaction eeptiens t0 this pp in thecolumn heedec1 Remarks? diluent. As will be appreciated, the rate ofreaction at The q y of amine salt and the p ifi amine l are temperaturesof from --30 C. to 0 C. will he somevaried as indicated therein and thepercentage of yield what slow. The minimum temperature for the processof is based on the monochlorobenzene charged.

Table 1 Moles amine Percent Example Amine salt salt pet-mole Percentpara Remarks oi chloroyield isomer benzene 2 pyridine sulfate 0.25 9067. 4 Reaction time 2 hours. 3 2-plcolme sulfate 0.25 90 67.8 o.

quinoline sulfate 0.175 95 67.4 Reaction time 2 hours and 0.25 moleexcess of HhgOi as mixed acid 5 nicotinic acid sulfate o. 5 95 70, 6 18use 6... t-butylamine sulfate 0.2 95 68 7- do. 1.0 as 71 8. .d0. 3.0 709. .do 4.0 72 10-. triethylamlne sulfate 0.73 96 70 11 trimethylaminesulfate.-. 1.0 65

this invention is therefore that temperature just above that EXAMPLE 12at which no reaction between the nitrating agent and the halobenzenewill take place. The maximum temperature is only of economic importance,for it is dependent on economic factors rather than technical factors.For ex ample, some of the aliphatic amine salts will begin to oxidize attemperatures above 100 C. and in addition, it is necessary to supplyconsiderable amounts of heat to achieve and maintain reactiontemperatures above 90 C. Temperatures within the range of from about 30C. to about 90 C. are desirably used, while temperatures within therange of from C. to C. are especially preferred.

After the nitration reaction is complete, the product can berecoveredfrom the reaction by any method well known to those skilled in the art.For example, the reaction mixture is permitted to settle into twophases, i.e. an organic phase and an aqueous phase. The organic phase isthen separated and the aqueous phase which con The procedure of Example1 is repeated except that an equivalent amount of a mixed acidcontaining 36% nitric acid, 59% sulfuric acid and 5% water is used inplace of the 33/55 mixed acid. The para isomer content of the product isabout 73%.

EXAMPLE 14 The procedure of Example 1 is repeated except that anequivalent amount of pyridine nitrate is substituted for the pyridinesulfate of said example. Similar results are obtained in that theproduct contains about of the para isomer of nitrochlorobenzene.

EXAMPLE 15 The procedure of Example 1 is repeated except that anequivalent amount of a mixed acid containing 27% nitric acid, 59%sulfuric acid and 14% water is substituted for the 33/55 mixed acid. Thepara isomer content of the product is about 70%.

EXAMiLE 16 The procedure of Example 1 is repeated using in place of thepyridine sulfate, a stoichiometrically equivalent amount of a sulfatesalt of each of the following amines:

In each instance the para isomer content of the prodnot is about 70%.

Dimethylamine Ethylenediamine N-ethyl-pentadecylamine Butylamine 1,l-dimethylpropylamine 1,1-dimethylbutylamine 1,1-dimethylpentylamineCyclohexylamine N,N-diethylcyclohexylamine 2,6-dimethylcyclohexylamineDicyclohexylamine Pyrrolidine Imidazole 1,2,3-triazole 2-pipeco1ine2,6-dimethylpiperidine 5-ethyl-2-methylpiperidine 4-methylpiperazine 3,5-dimethylmorpholine Morpholine Azi-ridine Thiarnorpholine isoquinolineAcridine Phenanthridine t-Dodecylamine t-Tetradecylamine t-Octylaminet-Octadecylamine t-Hexadecylamine EXAMPLE 17 The procedure of Example 10is repeated using in place of the triethylamine sulfate about 1 mole ofthe sulfate salt per mole of chlorobenzene of each of the followingtrialkylamines:

(1) Tributylamine (2) Tripropylamine (3) Triisopropylamine (4) N-ethyldipropylamine (5) N,N-diethylbutylamine In each case the para isomercontent of the product is in excess of 70%. From the results obtained itis clear that trialkylamines wherein the alkyl groups each contain from2 to 4 carbon atoms also constitute a preferred class of amine salts tobe employed in the process of this invention.

While this invention has been described with respect to certainembodiments, it is not so limited and it is to be understood thatvariations and modifications thereof which are obvious to those skilledin the art may be made without departing from the spirit or scope ofthis invention.

What is claimed is:

1. In a process for the nitration of halobenzene, the improvement whichcomprises carrying out the nitration in the presence of an acid salt ofan amine wherein the acid portion is derived from an acid of the groupcon sisting of nitric acid and sulfuric acid, said acid salt beingpresent in an amount which is snflicient to produce a para directiveeffect.

2. A process of claim 1 wherein the nitrating agent is a mixturecomprising nitric acid and sulfuric acid.

a 3. In a process for the mixed acid nitration of chlorobenzene, theimprovement which comprises carrying out the nitration in the presenceof an amine sulfate in an amount which is suiiicient to produce a paradirective effect.

4. A process of claim 3 wherein the amine sulfate is derived from aheterocyclic amine.

5. In a process for the mixed acid nitration of chlorobenzene, theimprovement which comprises carrying out the nitration in the presenceof a sulfate salt of a tertiary alkyl amine of the formula wherein R isan alkyl radical having from 1 to 18 carbon atoms, said sulfate saltbeing present in an amount which is sufficient to produce a paradirective effect.

6. In a process for the mixed acid nitration of chiorobenzene, theimprovement which comprises carrying out the nitration in the presenceof a sulfate salt of a trialkyl amine wherein each alkyl group has from2 to 4 carbon atoms, said sulfate salt being present in an amount whichis sufiicient to produce a para directive effect.

7. A process for the production of nitrochlorobenzene which comprisesreacting monochlorobenzene with a mixed acid comprising from about 30%to about 40% by weight of nitric acid and from about 65% to about 55% byWeight of sulfuric acid in the presence of from about 0.5 to 2.0 molesof an aliphatic amine sulfate per mole of monochlorobenzene.

8. A process for the production of nitrochlorobenzene which comprisesadding a stoichiometric quantity of a mixed acid, comprising from about30% to about 40% by weight of nitric acid and from about 65% to about55% by weight of sulfuric acid, to a reaction zone containingmonoshlorobenzene and a sulfate salt of an aliphatic amine, the quantityof amine sulfate being Within the range of from about 0.5 to about 2moles per mole of monochlorobenzene.

9. A process of claim 8 wherein the aliphatic amine sulfate is derivedfrom a tertiary alkylamine of the formula wherein R is an alkyl radicalcontaining from 1 to 18 carbon atoms.

10. A process of claim 9 wherein the nitrating temperature is within therange of from 50 C. to 60 C.

11. A process of claim 8 wherein the amine sulfate is tertiarybutylamine sulfate.

12. A process of claim 8 wherein the aliphatic amine sulfate is derivedfrom a trialkylamine wherein each alkyl group contains from 2 to 4carbon atoms.

13. A process of claim 11 wherein the nitrating temperature is withinthe range of from 50 C. to 60 C.

14. A process of claim 12 wherein the amine sulfate is triethylaminesulfate.

15. A process for the production of nitrochlorobenzene which comprisesadding a stoichiometric quantity of a mixed acid comprising from about30% to about 40% by weight of nitric acid and from about 65% to about 55by weight of sulfuric acid to a reaction zone con tainingmonochlorobenzene and a sulfate salt of a heterocyclic amine, the totalquantity of sulfate salt being within the range of from about 0.5 toabout 2 moles per mole of mo-nochlorobenzene and maintaining thetemperature within the range of from about 30 C. to about C. throughoutthe nitration reaction.

16. A process of claim 14 wherein the nitrating tem- 19. A process ofclaim 15 wherein the sulfate salt is perature is within the range offrom 50 C. to 60 C. 2-pico1ine sulfate.

17. A process of claim 15 wherein the sulfate salt is pyridine sulfate.

18. A process of claim 15 wherein the sulfate salt is 5 quinolinesulfate.

References Cited in the file of this patent UNITED STATES PATENTS MaresFeb. 27, 1945 Cherlow et a1. Jan. 18, 1955

1. IN A PROCESS FOR THE NITRATION OF HALOBENZENE, THE IMPROVEMENT WHICHCOMPRISES CARRYING OUT THE NITRATION IN THE PRESENCE OF AN ACID SALT OFAN AMINE WHEREIN THE ACID PORTION IS DERIVED FROM AN ACID OF THE GROUPCONSISTING OF NITRIC ACID AND SULFURIC ACID, SAID ACID SALT BEINGPRESENT IN AN AMOUNT WHICH IS SUFFICIENT TO PRODUCE A PARA DIRECTIVEEFFECT.